1. Field of the Invention
Embodiments of the present invention relate generally to a blanking device for multi charged particle beams, and a multi charged particle beam writing apparatus, and more specifically, to a blanking device to be mounted in a multi-beam writing apparatus, for example.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer, etc. with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time (one shot) in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multi-beams are formed by letting portions of an electron beam emitted from an electron gun assembly pass through a corresponding hole of a plurality of holes in the mask, a blanking control is provided for each of the beams, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is separately controlled based on an irradiation time. For highly accurately controlling such a dose of each beam, it is necessary to perform high speed blanking control to provide an ON or OFF state of each beam. In a writing apparatus of a multi-beam system, there is mounted a blanking plate where passage holes for multi-beams are formed, and at the circumference of each of the passage holes, a pair of blanking electrodes (blanker) and a blanking control circuit (LSI circuit) for each of the multi-beams are arranged. Using the MEMS (Micro Electro Mechanical Systems) technique, the blanking plate is fabricated by forming the passage holes, a plurality of pairs of blanking electrodes, etc. on a silicon (Si) substrate. Conventionally, insulators are exposed on the upper surface of the blanking plate. Therefore, the insulators on the upper surface are charged when beams irradiate the surface, thereby resulting in beam distortion or blur. Moreover, an overvoltage occurs in the blanking electrode because of the charging, which causes breakage of the blanking control circuit formed on the blanking plate.
There is disclosed a blanking plate whose surface is covered with a metal film and in which bonding connection using indium (In) is provided between a multi-beam deflector array means, on the surface of which a metal pad is formed, and a silicon electrode, which is positioned/installed completely independently of the main body of the multi-beam deflector array means (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2010-267962). In this disclosure, a dielectric film is exposed over the whole circumference of the electrode, including the opening side through which beams pass. Therefore, the possibility remains that beam charging occurs in the dielectric film portion at the opening side.